Those who have physically died continue to live eternally in the spirit realms and are extremely interested in what happens here in the physical world. They are waiting patiently to be contacted by mediums who can deliver messages of wisdom.
Mediums generally bring ‘proof of spirit survival’ changing a person from a non-believer in life-after-death to a believer.
In ancient times, 'proof of survival' mediumship did not exist. It did not need to. Everyone believed in the afterlife because they were closer to the subtle realms than we are in the busy world of the 21st century.